Water Journal : Water Journal September 2012-1
rural pipeline management refereed paper 74 SEPTEMBER 2012 water technical features Abstract Large, unfiltered water pipe networks have been constructed and operated for the past two years to replace a leaky open channel system in the Grampians Wimmera Mallee Region. Significant water quality risks have emerged as well as a number of new opportunities for improved treatment, environmental management and local recreation. This paper summarises these and complements other recent published studies. (Barton et al., 2009; Mitra et al., 2012). Introduction Grampians Wimmera Mallee Water (GWMWater) owns and operates an extensive network of rural pipelines that supply untreated water to a wide range of customers in the Wimmera and Mallee regions of Western Victoria (Figure 1). The rural pipeline network comprises the Wimmera Mallee Pipeline (WMP) and the Northern Mallee Pipeline (NMP), each of which is comprised of discrete supply systems. GWMWater engaged and worked with GHD on various investigations and design aspects of these projects. Water is supplied by this network to towns, rural properties, industries, recreational lakes and wetlands. This water is further treated for supply as drinking water to 27 towns throughout this region. The network comprises approximately 8,800km of pipelines, covering approximately 2 million ha, or about 10% of Victoria (Mala-Jetmarova et al., 2011). The pipe network was constructed to replace an ageing network of channels across the region that was characterised by poor water efficiency due to high losses from seepage and evaporation. Water is supplied from Lake Bellfield (78,560ML capacity) and Taylors Lake in the Grampians in the south and from the Murray River in the north. This large pipe network is achieving its objectives in terms of energy-efficient and reliable delivery of sufficient quantity of water with minimal losses. Possible water savings have been previously estimated at close to 103GL per year (Barton et al., 2009). However, because the water is not filtered, a number of water quality risks have emerged, particularly following the very high rainfall/runoff conditions since early 2011. This paper discusses these water quality risks, in particular the build-up of sediments, iron and manganese slimes and biological infestations that can cause increased hydraulic losses and block pump strainers and customer filters (Mitra et al., 2012). It also summarises the new environmental/recreational/ water treatment opportunities that have emerged with the establishment of this rural pipe network. Finally, the paper summarises key future directions GWMWater is pursuing to improve management of the WMP and NMP. A Key Risk: Pipe Fouling GWMWater was aware from early experience operating the NMP that fouling of internal pipe surfaces by biological or chemical material could cause operational problems including increased hydraulic losses, fouling of downstream customer meters and even water quality events if the fouling material was to be scoured from the pipe walls. Typically pipe fouling is a combination of: • Iron and manganese slimes Dissolved iron and manganese can form a slime that deposits on pipe walls, which in turn can scour and cause dirty water events for downstream customers. Water sourced from reservoirs that stratify is a typical source of these slimes. • Sediment-based deposits Sediment particles can build up on walls as well as accumulate on the floor in pipelines over time, especially where raw water is turbid and pipe velocities are low. Scouring due to changes in flow can cause downstream water quality problems for treatment works and raw water customers due to sudden increases in turbidity and sediment that blocks water filters. P Carroll, M Chapman, A Barton, G Whorlow A case study in water quality risks, unintended consequences and opportunities EXPERIENCE WITH THE GRAMPIANS WIMMERA MALLEE PIPELINE SCHEME Figure 1. GWMWater's rural pipeline network.
Water Journal November 2012-1
Water Journal August 2012